"All jet exhausts do not create contrails. In warmer areas, contrails are rare, while in temperate areas, especially in the Midwest and Great Plains, contrails are common, especially in the winter and spring. Sometimes, the added moisture of a series of jets will increase the atmospheric humidity enough so that subsequent aircraft will form contrails even though earlier ones did not. "

Contrails alter temperature the same way that natural high clouds do. During the day, the layer of ice crystals shields the ground from some of the sun's energy. At night, the layer of ice crystals prevents some of Earth's heat from dissipating into the vacuum. Without the contrails, the daytime temperature would be slightly higher and the nighttime temperature would be slightly lower, creating the increased range between lowest and highest temperatures.